Everyone realizes the necessity of blood for life, and blood donors are considered the only source for patients who need blood transfusion, as it is not possible to manufacture blood. It also transports metabolic wastes away from these cells. In fact, there are four main components of human blood.The process of drawing blood is defined as collecting blood samples, and it is usually taken from a vein. This term is usually called the procedure used to collect a blood sample for laboratory tests. This process is done through several simple steps